This invention relates to a sensor rotor that rotates with a wheel for detecting wheel speed.
Many of today's automobiles are equipped with an antilock brake system (ABS) and/or a traction control system (TCS). ABS and TCS perform brake and slip control based on wheel speeds detected by sensors.
Some of such wheel speed sensors include sensor rotors each mounted on a wheel bearing.
This type of sensor rotor comprises a magnetized ring having opposite magnetic poles alternately formed in the circumferential direction thereof, and a press-in ring having a flange. The sensor rotor is mounted to a wheel bearing by press-fitting the press-in ring into the rotating race of the bearing and fixing the magnetized ring to the inner surface of the flange of the press-in ring.
A rotation sensor is mounted on the fixed race of the wheel bearing to detect the rotating speed of the rotating race and thus that of the wheel by detecting the electromotive force induced when the magnetic poles of the rotating magnetized ring pass by the sensor.
In a conventional method of manufacturing a sensor rotor, the magnetized ring is formed by blanking a ring out of a flat plate member made of a magnetizable material, and magnetizing the ring. The portion of the flat plate inside of the ring is totally useless and is discarded as a waste.
In another conventional method, four ring pieces, which are quarter arcs of a ring, are formed by blanking a magnetic plate, the ends of the ring pieces are welded together to form a ring, and the ring is magnetized to form opposite magnetic poles alternately in the circumferential direction thereof.
Since the ring pieces have outer edges which have smaller radius or curvature curvature than their inner edges, they cannot be arranged with no space formed between the outer and inner edges of adjacent ring pieces. Thus, when such ring pieces are blanked out of a flat plate material, marginal portions inevitably remain between the outer and inner edges of the adjacent ring pieces. Such marginal portions of the flat plate material are useless and thus have to be discarded as waste.
Thus, in either of the above conventional methods, material loss is inevitable.
An object of this invention is to eliminate such material loss and thus reduce the manufacturing cost of a sensor rotor.